The present invention relates to a scanning System for a heavy ion gantry used in a heavy ion cancer therapy facility according to the subject matter of claim 1.
From U.S. Pat. No. 4,870,287 a proton beam therapy system is known for selectively generating and transporting proton beams from a single proton source and accelerator to selected ones of a plurality of patient treatment stations each having a rotatable gantry for delivering the proton beam at different angles to patients supported in fixed orientations at the stations.
Further it is known from U.S. Pat. No. 4,870,287 a new imaging technique like a computed tomography scanning which uses a scanning technique to identify the exact location of the site to be treated, but there is no hint in U.S. Pat. No. 4,870,287 for applying a scanning magnet to directly and precisely move or bend the therapy beam to the exact location of the site to be treated.
From H. Eickhoff et al. xe2x80x9cThe proposed accelerator facility for light ion cancer therapy in Heidelbergxe2x80x9d (Proc. Of the IEEE Part. Acc. Conf. NY, 1999, p 2513-2515) an intensity-controlled raster scan technique is known to move or bend the ion beam of a therapy system. However, neither the scanning magnets are defined nor the position of these scanning magnets within the therapy system are disclosed.
Thus, it is an object of the present invention to define and provide a scanner magnet for a high energy ion beam used in a heavy ion cancer therapy facility. It is particularly an object of the present invention to provide a combination of a scanner magnet positioned upstream a last bending magnet.
This object is achieved by the subject matter of independent claim 1. Features of preferred embodiments are disclosed by dependent claims.
According to the present invention a scanning System for a heavy ion gantry is provided comprising a scanner magnet for a high energy ion beam used in a heavy ion cancer therapy facility having a maximal bending angle (xcex1) of about 1.5 degree; a curvature radius of about 22 m; a path length of about 0.6 m and a gap height (h) and a gap width (w) in the range of 120 mm to 150 mm. Further each scanner magnet (1-2, 3-4) comprises one glued yoke element made of steel plates having a thickness of up to 0.3 mm and being alloyed with up to 2% silicon. This yoke element has a width in the range of 300 mm to 400 mm, a height in the range of 200 mm to 250 mm and a length in the range of 500 to 600 mm. A coil for each scanner magnet has a number of windings in the range of 50 to 70. Further the system comprises a 90 degree Dipole positioned downstream of said scanner magnets having an aperture adapted to the scanning area, and enclosing a yoke element with gaps to increase the homogeneity of the electric field. Additionally the system encloses beam diagnostic plate type detectors stapled downstream of said 90 degree bending magnet.
Such a scanning system has the advantage that it controls the direction of an ion beam at the location of the ISO-plane or ISO-center over a scan field of 200xc3x97200 mm, when at least two scanning magnets are applied as horizontal and vertical dipole magnets.
In a preferred embodiment said scanning magnets are positioned within a gantry system of a heavy ion cancer therapy system upstream of the last 90 degree bending magnet. This position has the advantage that the space for the patient treatment position is not decreased or limited by the volume of the scanning magnets. The overall radius of the Gantry is minimized and the Gantry weight is decreased. Said scanning magnets in combination with said a 90 degree bending dipole having an appropriate yoke with defined gaps and an appropriate exit edge angle a parallel scanning downstream said 90 degree bending dipole is possible.
Preferably the coil of said scanner magnet is designed to tolerate a maximum coil current in the range of 500 to 600 A. Such a high coil current is supplied to said 50 to 70 turns of said coil, to perform a maximum bending angle of the ion beam of about 1.5 degree.
To manage the heat loss of such a coil the scanner magnet is water-cooled by plurality of cooling channels preferably by at least six cooling channels and preferably by a total cooling water supply in the range of 5 l/min to 10 l/min. Such a water cooled coil has the advantage to increase the safety of operation during patient treatment compared to Hydrogen or Nitrogen cooled super conductive coils.
In a further preferred embodiment the coil is not super-conductive but has a coil resistance in the range of 30 mxcexa9 and 50 mxcexa9 which causes a maximum DC-power consumption in the range of 10 KW to 12 KW.
To guarantee said maximum bending angle the total coil inductance of said scanner magnet is in the range of 3 to 4 mH.
The total supply voltage for the coil is preferably in the range of xc2x1350 V to xc2x1400 V to maintain the maximum coil current in each bending direction.
In a further preferred embodiment said scanner magnet comprises one single yoke-segment. This has the advantage of a simple construction and an easy maintenance and assembly-handling of the scanner system which minimizes the operational costs.
The 90 degree dipole provides a homogeneity of the electric field of about +xe2x88x922xc3x9710xe2x88x924. Such a homogeneity of the electric field avoids image errors and elliptic beam spots. The gaps within the yoke of the bending dipole has the advantage, that the homogeneity of such a large scanning area of 23xc3x9723 cm is in the above mentioned limits at the ISO center of the gantry.
Since there might occur saturation effects at the exit of the 90 degree bending Dipole having such edge angles, the Yoke cross section is locally increased. Further the maximum electric field is limited to 1.8 Tesla to minimize the saturation effects.
The overall weight of the bending dipole is about 72 t. The Yoke is divided into 6 segments each having four adjustment means.